A swimming pool can be filled by pipe A in 3 hours and by pipe B in 6 hours, each pump working on its own. At 9 am, pump A is started. At what time will the swimming pool be filled if pump B is started at 10 am?
Let pool volume be 30 litres.
Flow rate through A = 30/3 = 10 litres/hr
Flow rate through B = 30/6 = 5 litres/hr
A is opened at 9:00am and then B is opened at 10:00 am. So, A alone fills the tank for an hour to 10 litres.
After 10:00am both are opened simultaneously.
Remaining 20 litres of the pool are filled at a combined flow rate of 15 litres/hr which takes 80 min to get filled.
$$\therefore\ $$ The pool is filled 80 mins after 10:00am i.e. 11:20am
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